| Message ID | 20181205023426.24029-1-richard.weiyang@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] admin-guide/memory-hotplug.rst: remove locking internal part from admin-guide | expand |
On 05.12.18 03:34, Wei Yang wrote: > Locking Internal section exists in core-api documentation, which is more > suitable for this. > > This patch removes the duplication part here. > > Signed-off-by: Wei Yang <richard.weiyang@gmail.com> > --- > Documentation/admin-guide/mm/memory-hotplug.rst | 40 ------------------------- > 1 file changed, 40 deletions(-) > > diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst > index 5c4432c96c4b..241f4ce1e387 100644 > --- a/Documentation/admin-guide/mm/memory-hotplug.rst > +++ b/Documentation/admin-guide/mm/memory-hotplug.rst > @@ -392,46 +392,6 @@ Need more implementation yet.... > - Notification completion of remove works by OS to firmware. > - Guard from remove if not yet. > > - > -Locking Internals > -================= > - > -When adding/removing memory that uses memory block devices (i.e. ordinary RAM), > -the device_hotplug_lock should be held to: > - > -- synchronize against online/offline requests (e.g. via sysfs). This way, memory > - block devices can only be accessed (.online/.state attributes) by user > - space once memory has been fully added. And when removing memory, we > - know nobody is in critical sections. > -- synchronize against CPU hotplug and similar (e.g. relevant for ACPI and PPC) > - > -Especially, there is a possible lock inversion that is avoided using > -device_hotplug_lock when adding memory and user space tries to online that > -memory faster than expected: > - > -- device_online() will first take the device_lock(), followed by > - mem_hotplug_lock > -- add_memory_resource() will first take the mem_hotplug_lock, followed by > - the device_lock() (while creating the devices, during bus_add_device()). > - > -As the device is visible to user space before taking the device_lock(), this > -can result in a lock inversion. > - > -onlining/offlining of memory should be done via device_online()/ > -device_offline() - to make sure it is properly synchronized to actions > -via sysfs. Holding device_hotplug_lock is advised (to e.g. protect online_type) > - > -When adding/removing/onlining/offlining memory or adding/removing > -heterogeneous/device memory, we should always hold the mem_hotplug_lock in > -write mode to serialise memory hotplug (e.g. access to global/zone > -variables). > - > -In addition, mem_hotplug_lock (in contrast to device_hotplug_lock) in read > -mode allows for a quite efficient get_online_mems/put_online_mems > -implementation, so code accessing memory can protect from that memory > -vanishing. > - > - > Future Work > =========== > > I reported this yesterday to Jonathan and Mike https://lkml.org/lkml/2018/12/3/340 Anyhow Reviewed-by: David Hildenbrand <david@redhat.com>
On Wed, Dec 05, 2018 at 09:03:24AM +0100, David Hildenbrand wrote: > On 05.12.18 03:34, Wei Yang wrote: > > Locking Internal section exists in core-api documentation, which is more > > suitable for this. > > > > This patch removes the duplication part here. > > > > Signed-off-by: Wei Yang <richard.weiyang@gmail.com> > > --- > > Documentation/admin-guide/mm/memory-hotplug.rst | 40 ------------------------- > > 1 file changed, 40 deletions(-) > > > > diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst > > index 5c4432c96c4b..241f4ce1e387 100644 > > --- a/Documentation/admin-guide/mm/memory-hotplug.rst > > +++ b/Documentation/admin-guide/mm/memory-hotplug.rst > > @@ -392,46 +392,6 @@ Need more implementation yet.... > > - Notification completion of remove works by OS to firmware. > > - Guard from remove if not yet. [ ... ] > > Future Work > > =========== > > > > > > I reported this yesterday to Jonathan and Mike > > https://lkml.org/lkml/2018/12/3/340 Somehow I've missed it... > Anyhow > > Reviewed-by: David Hildenbrand <david@redhat.com> Acked-by: Mike Rapoport <rppt@linux.ibm.com> > > -- > > Thanks, > > David / dhildenb >
On Wed, Dec 05, 2018 at 09:03:24AM +0100, David Hildenbrand wrote: >On 05.12.18 03:34, Wei Yang wrote: >> Locking Internal section exists in core-api documentation, which is more >> suitable for this. >> >> This patch removes the duplication part here. >> >> Signed-off-by: Wei Yang <richard.weiyang@gmail.com> >> --- >> Documentation/admin-guide/mm/memory-hotplug.rst | 40 ------------------------- >> 1 file changed, 40 deletions(-) >> >> diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst >> index 5c4432c96c4b..241f4ce1e387 100644 >> --- a/Documentation/admin-guide/mm/memory-hotplug.rst >> +++ b/Documentation/admin-guide/mm/memory-hotplug.rst >> @@ -392,46 +392,6 @@ Need more implementation yet.... >> - Notification completion of remove works by OS to firmware. >> - Guard from remove if not yet. >> >> - >> -Locking Internals >> -================= >> - >> -When adding/removing memory that uses memory block devices (i.e. ordinary RAM), >> -the device_hotplug_lock should be held to: >> - >> -- synchronize against online/offline requests (e.g. via sysfs). This way, memory >> - block devices can only be accessed (.online/.state attributes) by user >> - space once memory has been fully added. And when removing memory, we >> - know nobody is in critical sections. >> -- synchronize against CPU hotplug and similar (e.g. relevant for ACPI and PPC) >> - >> -Especially, there is a possible lock inversion that is avoided using >> -device_hotplug_lock when adding memory and user space tries to online that >> -memory faster than expected: >> - >> -- device_online() will first take the device_lock(), followed by >> - mem_hotplug_lock >> -- add_memory_resource() will first take the mem_hotplug_lock, followed by >> - the device_lock() (while creating the devices, during bus_add_device()). >> - >> -As the device is visible to user space before taking the device_lock(), this >> -can result in a lock inversion. >> - >> -onlining/offlining of memory should be done via device_online()/ >> -device_offline() - to make sure it is properly synchronized to actions >> -via sysfs. Holding device_hotplug_lock is advised (to e.g. protect online_type) >> - >> -When adding/removing/onlining/offlining memory or adding/removing >> -heterogeneous/device memory, we should always hold the mem_hotplug_lock in >> -write mode to serialise memory hotplug (e.g. access to global/zone >> -variables). >> - >> -In addition, mem_hotplug_lock (in contrast to device_hotplug_lock) in read >> -mode allows for a quite efficient get_online_mems/put_online_mems >> -implementation, so code accessing memory can protect from that memory >> -vanishing. >> - >> - >> Future Work >> =========== >> >> > >I reported this yesterday to Jonathan and Mike > >https://lkml.org/lkml/2018/12/3/340 > Ah, Thanks :-) > >Anyhow > >Reviewed-by: David Hildenbrand <david@redhat.com> > >-- > >Thanks, > >David / dhildenb
On Wed, Dec 05, 2018 at 10:30:13AM +0200, Mike Rapoport wrote: >On Wed, Dec 05, 2018 at 09:03:24AM +0100, David Hildenbrand wrote: >> On 05.12.18 03:34, Wei Yang wrote: >> > Locking Internal section exists in core-api documentation, which is more >> > suitable for this. >> > >> > This patch removes the duplication part here. >> > >> > Signed-off-by: Wei Yang <richard.weiyang@gmail.com> >> > --- >> > Documentation/admin-guide/mm/memory-hotplug.rst | 40 ------------------------- >> > 1 file changed, 40 deletions(-) >> > >> > diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst >> > index 5c4432c96c4b..241f4ce1e387 100644 >> > --- a/Documentation/admin-guide/mm/memory-hotplug.rst >> > +++ b/Documentation/admin-guide/mm/memory-hotplug.rst >> > @@ -392,46 +392,6 @@ Need more implementation yet.... >> > - Notification completion of remove works by OS to firmware. >> > - Guard from remove if not yet. > >[ ... ] > >> > Future Work >> > =========== >> > >> > >> >> I reported this yesterday to Jonathan and Mike >> >> https://lkml.org/lkml/2018/12/3/340 > >Somehow I've missed it... > >> Anyhow >> >> Reviewed-by: David Hildenbrand <david@redhat.com> > >Acked-by: Mike Rapoport <rppt@linux.ibm.com> > Thanks :-) >> >> -- >> >> Thanks, >> >> David / dhildenb >> > >-- >Sincerely yours, >Mike.
On Wed 05-12-18 10:34:25, Wei Yang wrote: > Locking Internal section exists in core-api documentation, which is more > suitable for this. > > This patch removes the duplication part here. > > Signed-off-by: Wei Yang <richard.weiyang@gmail.com> Yes this doesn't really make any sense in an admin guide. It is a pure implementation detail nobody should be relying on.
diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst index 5c4432c96c4b..241f4ce1e387 100644 --- a/Documentation/admin-guide/mm/memory-hotplug.rst +++ b/Documentation/admin-guide/mm/memory-hotplug.rst @@ -392,46 +392,6 @@ Need more implementation yet.... - Notification completion of remove works by OS to firmware. - Guard from remove if not yet. - -Locking Internals -================= - -When adding/removing memory that uses memory block devices (i.e. ordinary RAM), -the device_hotplug_lock should be held to: - -- synchronize against online/offline requests (e.g. via sysfs). This way, memory - block devices can only be accessed (.online/.state attributes) by user - space once memory has been fully added. And when removing memory, we - know nobody is in critical sections. -- synchronize against CPU hotplug and similar (e.g. relevant for ACPI and PPC) - -Especially, there is a possible lock inversion that is avoided using -device_hotplug_lock when adding memory and user space tries to online that -memory faster than expected: - -- device_online() will first take the device_lock(), followed by - mem_hotplug_lock -- add_memory_resource() will first take the mem_hotplug_lock, followed by - the device_lock() (while creating the devices, during bus_add_device()). - -As the device is visible to user space before taking the device_lock(), this -can result in a lock inversion. - -onlining/offlining of memory should be done via device_online()/ -device_offline() - to make sure it is properly synchronized to actions -via sysfs. Holding device_hotplug_lock is advised (to e.g. protect online_type) - -When adding/removing/onlining/offlining memory or adding/removing -heterogeneous/device memory, we should always hold the mem_hotplug_lock in -write mode to serialise memory hotplug (e.g. access to global/zone -variables). - -In addition, mem_hotplug_lock (in contrast to device_hotplug_lock) in read -mode allows for a quite efficient get_online_mems/put_online_mems -implementation, so code accessing memory can protect from that memory -vanishing. - - Future Work ===========
Locking Internal section exists in core-api documentation, which is more suitable for this. This patch removes the duplication part here. Signed-off-by: Wei Yang <richard.weiyang@gmail.com> --- Documentation/admin-guide/mm/memory-hotplug.rst | 40 ------------------------- 1 file changed, 40 deletions(-)